assertion error

compute.py

@@ -1,6 +1,13 @@
-"""Matrix multiplication with explicit dimension checks."""
+"""Matrix multiplication with explicit dimension checks.
 
-#ergänzter kommentar
+This module provides a pure‑Python implementation that
+- validates input dimensions and structure
+- performs generic matrix multiplication without external libs
+- raises informative ``ValueError`` when inputs are inconsistent.
+
+The implementation is small but fully typed so it can be
+imported into other projects or used as a teaching example.
+"""
 
 from __future__ import annotations
 
@@ -23,23 +30,33 @@ def matmul(left: Matrix, right: Matrix) -> list[list[float]]:
         ValueError: If either input is empty, ragged, or if
             cols_left != rows_right.
     """
+    # Validate first matrix (rows and columns), raise if invalid.
     _validate(left, "left")
+    # Validate second matrix for similar conditions.
     _validate(right, "right")
 
+    # Number of columns in left matrix.
     cols_left = len(left[0])
+    # Number of rows in right matrix.
     rows_right = len(right)
+    # Ensure the inner dimensions are compatible.
     if cols_left != rows_right:
         raise ValueError(
             f"dimension mismatch: left has {cols_left} columns, "
             f"right has {rows_right} rows"
         )
 
+    # Number of columns in right matrix.
     cols_right = len(right[0])
+    # Prepare result container: rows of left × columns of right.
     result: list[list[float]] = []
+    # Iterate over rows of left matrix.
     for i in range(len(left)):
         row: list[float] = []
+        # Iterate over columns of right matrix.
         for j in range(cols_right):
             total = 0.0
+            # Accumulate dot product of row i of left and column j of right.
             for k in range(cols_left):
                 total += left[i][k] * right[k][j]
             row.append(total)
@@ -47,8 +64,20 @@ def matmul(left: Matrix, right: Matrix) -> list[list[float]]:
     return result
 
 
+
+
+    # Helper to validate a matrix is non‑empty and rectangular.
 def _validate(matrix: Matrix, name: str) -> None:
-    """Check that *matrix* is a non-empty, rectangular 2D sequence."""
+    """Check that *matrix* is a non‑empty, rectangular 2D sequence.
+
+    Validation rules:
+    *  The outer sequence must contain at least one row.
+    *  Every row must have the same number of columns.
+    *  No empty rows are allowed.
+
+    Raises:
+        ValueError: If the matrix is empty, has zero columns, or is ragged.
+    """
     if len(matrix) == 0:
         raise ValueError(f"{name} matrix is empty")
     width = len(matrix[0])
@@ -61,6 +90,36 @@ def _validate(matrix: Matrix, name: str) -> None:
                 f"row {index} has {len(row)}"
             )
 
+def transpose(matrix: Matrix) -> list[list[float]]:
+    """Transponiere die gegebene Matrix.
+
+    Alle Zeilen werden zu Spalten und alle Spalten zu Zeilen.
+
+    Parameters
+    ----------
+    matrix
+        Matrix in Form ``Sequence[Sequence[float]]``.
+
+    Returns
+    -------
+    list[list[float]]
+        Die transponierte Matrix.
+
+    Raises
+    ------
+    ValueError
+        Wenn ``matrix`` leer ist oder nicht gleichmäßig viele Spalten
+        in den Zeilen hat.
+    """
+    _validate(matrix, "matrix")
+    rows = len(matrix)
+    cols = len(matrix[0])
+    transposed: list[list[float]] = []
+    for c in range(cols):
+        new_row: list[float] = []
+        for r in range(rows):
+            new_row.append(matrix[r][c])
+        transposed.append(new_row)
 
 if __name__ == "__main__":
     # Example 1: standard 2x3 * 3x2 multiplication.
@@ -101,3 +160,53 @@ if __name__ == "__main__":
         print("example 3 passed:", error)
 else:
     raise AssertionError("example 3 failed: no ValueError raised")
+
+if __name__ == "__main__":
+    # Example 1: standard 2x3 * 3x2 multiplication.
+    a = [
+        [1, 2, 3],
+        [4, 5, 6],
+    ]
+    b = [
+        [7, 8],
+        [9, 10],
+        [11, 12],
+    ]
+    expected = [
+        [58, 64],
+        [139, 154],
+    ]
+    assert matmul(a, b) == expected, f"example 1 failed: {matmul(a, b)}"
+    print("example 1 passed:", matmul(a, b))
+
+    # Example 2: multiplication with the identity matrix changes nothing.
+    identity = [
+        [1, 0, 0],
+        [0, 1, 0],
+        [0, 0, 1],
+    ]
+    c = [
+        [2, -1, 0],
+        [0, 3, 4],
+        [5, 6, -2],
+    ]
+    assert matmul(c, identity) == c, "example 2 failed"
+    print("example 2 passed:", matmul(c, identity))
+
+    # Example 3: mismatched dimensions must raise ValueError.
+    try:
+        matmul([[1, 2, 3]], [[1, 2]])
+    except ValueError as error:
+        print("example 3 passed:", error)
+    else:
+        raise AssertionError("example 3 failed: no ValueError raised")
+
+    # Example 4: Demonstration of the transpose function.
+    example_matrix = [[1, 2, 3], [4, 5, 6]]
+    transposed = transpose(example_matrix)
+    print("Example 4: transpose([[1,2,3],[4,5,6]]) =", transposed)
+    assert transposed == [[1, 4], [2, 5], [3, 6]], "Example 4 failed"
+    print("example 4 passed")
+
+
+